1. Field of the Invention
The present invention relates to an image reading apparatus and an information processing apparatus having an image reading function. More particularly, the invention relates to an image reading apparatus and an information processing apparatus, which are provided with means for correcting read-out image signals.
2. Related Background Art
Among recording apparatuses, there has hitherto been the one having a mechanism to read out images on a document (a sheet), which is carried in the same manner as a recording medium, besides a mechanism to record on a recording medium (a sheet). As a recording apparatus provided with such reading function, there is an apparatus that reads a document (a sheet) arranged on a platen using image reading means (an image reading head) mounted on a carriage of the apparatus.
An apparatus of the kind has an advantage that it can be made smaller at lower costs, because images are read by scanning the surface of a document while making the image reading head and a document having such images movable by means of a sheet feeding mechanism and a carriage mechanism adopted for such apparatus. These image reading apparatuses are disclosed in the specifications of Japanese Patent Laid-Open Application No. 59-99860, Japanese Patent Laid-Open Application No. 59-99864, and Japanese Patent Laid-Open Application No. 59-228464, among others, for example. Also, it is disclosed that a white reference reflection plate is provided in a image reading position of a recording apparatus in order to correct the so-called shading distortion, that is, to correct the relationship between the output of reading by an image reading head (means for reading out images), and the black and white condition of a document (reflective densities).
However, for a structure where a white reference reflection plate is provided in the interior of a recording apparatus, the reference reflection plate tends to be stained because the paper and dust particles adhering to a carrier roller or the like are transferred to the reflection plate. Particularly, in a case of an ink jet recording apparatus that records by discharging ink to a recording medium, the white reference reflecting plate is stained by ink mist. As a result, it often becomes difficult for the reference plate to execute its essential function of correcting the shading distortion created by an image reading head.
Here, therefore, a method has been proposed for correcting the shading distortion that may be created by an image reading head, whereby to correct image signals to be output after conversion by use of an image reading head in such a manner that a white reference reflection sheet, which has been prepared separately, is inserted into the sheet carrying path, and the white reference reflection sheet is being carried and read out by the image reading head for the intended correction in the same way as a document to be read, while the white reference reflection sheet is pinched by a carrier roller and a pinch roller on its feeding side (the trailing end side in the carrying direction), and pinched by a pair of sheet expelling rollers or by a pair of a sheet expelling roller and a spur on its expelling side simultaneously.
However, in such method for correcting the shading distortion, ink often adheres to the sheet expelling roller, the spur, or others because these rollers are in contact with a recording medium (a sheet) at the time of recording, and the ink thus adhering to the rollers are transferred to the white reference reflection sheet, thus causing the reflective densities thereof to change (the closer to white, the smaller the value of the reflective density becomes and on the contrary, the closer to black, the greater becomes the value of the reflective density). As a result, the quality of an image to be read may be made inferior. Therefore, in order to remove the cause of such stains that may change the reflective densities it is required to replace the white reference reflection sheets or cleaning the white reference reflection sheet periodically. Furthermore, if a spur is used, there is a possibility that a white reference reflection sheet is damaged by the spur because the contact tips thereof are sharp.